Miniature helical resonators

ABSTRACT

A helical coil resonator is wound on a dielectric form mounted on a dielectric base. Four posts are mounted on the base at the corners of a square, and are threaded on their inner faces to form a threaded receptacle that is concentric about the coil. A cup-shaped dielectric tuning element is threaded in the receptacle for movement toward and away from the coil, and a metallic can is positioned around the posts. The capacity between the coil and can, and hence the resonant frequency of the resonator, is varied by adjusting the position of the tuning element relative to the coil.

United States Patent [72] Inventors Frederick E. Spangler;

Henry A. Schaefer, both of Lynchburg, Va. [21] Appl. No. 794,332 [22] Filed Jan. 27, 1969 [45] Patented May 25,1971 [73] Assignee General Electric Company [54] MINIATURE HELICAL RESONATORS 7 Claims, 3 Drawing Figs.

[52] US. Cl 333/705, 333/76, 333/82, 336/136 [51] Int. Cl 1103b 1/00, H03h 5/08 [50] Field of Search 333/705, 76, 82

[56] References Cited UNITED STATES PATENTS 2,227,846 1/1941 Rust 333/82 2,753,530 7/1956 Horvath 333/82X 2,889,522 6/1959 Friberg... 33/70(S)X 3,060,394 10/1962 Macda 336/136 3,092,796 6/1963 Maedam, 336/136X 3,409,850 11/1968 Oshima 333/76X Primary Examiner-Herman Karl Saalbach Assistant Examiner-Wm. N. Punter Attorneys-James J. Williams, Frank L. Neuhauser and Oscar B. Waddell ABSTRACT: A helical coil resonator is wound on a dielectric form mounted on a dielectric base. Four posts are mounted on the base at the corners of a square, and are threaded on their inner faces to form a threaded receptacle that is concentric about the coil. A cup-shaped dielectric tuning element is threaded in the receptacle for movement toward and away from the coil, and a metallic can is positioned around the posts. The capacity between the coil and can, and hence the resonant frequency of the resonator, is varied by adjusting the position of the tuning element relative to the coil.

PATENTED m2 5 I971 INVENTORS HENRY A. SCHAEFER, 'FREDRICK E. SPANGLER.

W H ATTORNEY.

MINIATURE HELICAL RESONATORS BACKGROUND OF THE INVENTION Our invention relates to an improved coil construction, and particularly to an improved coil construction that provides a tunable resonator for relatively high radio frequencies.

Helical coils, particularly helical coils used for resonators find many applications in radio apparatus. Such coils represent a considerable portion of the cost of radio apparatus, and hence ways are constantly being sought to make such coils as inexpensive as possible. This is particularly true as the frequency of the radio apparatus increases, since such an increased frequency means a physically smaller coil that is more difficult to manufacture.

Accordingly, an object of our invention is to provide a new and improved coil construction for radio frequency apparatus.

Another object of our invention is to provide an improved coil construction that is relatively easy to manufacture, and hence is relatively inexpensive.

In addition to the above objects, it is desirable that a radio coil be easily coupled to an electrical circuit, particularly when the coil is used as a resonator. Further, the coil should have means for tuning such as by means of a capacitor, so that its resonant frequency can be adjusted. And finally, the coil construction, with its capacitor, should be mechanically small or compact and structurally strong.

Accordingly, another object of our invention is to provide an improved construction which permits a'radio coil to be easily coupled to an electrical circuit.

Another object of our invention is to provide an improved coil construction having a tunable capacitor for adjusting the resonant frequency of the coil.

Still another object of our invention is to provide an improved construction that provides a radio coil which is relatively compactand mechanically strong.

SUMMARY or THE INVENTION Briefly, these and other objects are achieved in accordance with our invention by a coil construction having a base of dielectric material. A coil is wound about a longitudinal axis and positioned on the base so that the longitudinal axis extends upward from the base. Preferably, the coil is wound on a dielectric form. A plurality of posts, preferably four arranged at the corners of a square, extend upward from the base around the coil. These posts have threads on their inner faces to form a threaded receptacle. A tuning element that is preferably cup-shaped is formed of dielectric material with external treads for fitting in the threaded receptacle, and is threadedly positioned in the receptacle. The tuning element can be moved toward or away from the coil by rotation of the tuning element in its threaded receptacle. A metallic element is positioned around the posts, preferably in the form of a can, and connected to one end of the coil. As the tuning element is moved toward and away from the coil, the amount of dielectric material between the coil and conductive element is varied, so that the capacity associated with the coil is also varied. This variable capacity can be used to adjust the resonant frequency of the coil to a selected value. The coil may be coupled to electrical circuits by a window or opening in the conductive element, or by other suitable means. Thus, our construction provides a coil which can be easily constructed and which can be easily adjusted to a selected resonant frequency.

BRIEF DESCRlPTlON OF THE DRAWING The subject matter which we regard as our invention is particularly pointed out and distinctly claimed in the claims. The structure and operation of our invention, together with further objects and advantages, may be better understood from the following description given in connection with the accompanying drawing, in which:

FIG. 1 shows an exploded perspective view of a coil construction in accordance with our invention;

FIG. 2 shows a longitudinal cross-sectional view of our coil construction taken along a plane passing through diagonally opposite posts; and

FIG. 3 shows one equivalent electrical circuit of our coil construction of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIGS. 1 and 2, our coil construction comprises a square base 10 having four posts 11 a, 11 b, 11 c, 11 d extending upward from the base 10. Weprefer four posts positioned at the corners of a square since they provide good support and a compact arrangement from a space-utilization standpoint. The posts 11 a, 11 b, 11 c, 11 d are preferably formed integrally with the base 10 from a suitable dielectric material, such as polyphenylene oxide. The posts 11 a, 11 b, 11 c, 11 d are provided with threads 13 on their inner faces. The threads 13 are arranged so that they are positioned on a common helix to form a threaded receptacle. The base 10 is provided with a suitable hole or opening 14 for receiving a coil form 16.

The coil form 16 is a generally cylindrical structure having a helical groove or thread 17 extending along most of its length.

The coil form 16 is made of any suitable dielectric material, such as the polyphenylene oxide used for the base [0. A slot 18 is formed in the lower end of the coil form 16, and a longitudinal hole 19 is positioned at the upper end. A plurality of diametrically positioned slots 20 are positioned around the hole 19 at the upper end. When a coil is to be formed, and end 22 a of a length of wire 22 is placed in the slot 18, and the wire 22 is wound on an appropriate number of the grooves 17. The other end 22 b of the wire 22 is then passed through one of the slots 20 and cut off or bent, so that the wound coil is securely held on the coil form 16. After the coil is wound on the coil form 16, the lower end ofthe form 16 is inserted in the hole 14 in the base 10. The coil form 16 may be firmly held by cementing or other suitable fastening means.

A tuning element 25 is provided of suitable dielectric material, such as the polyphenylene oxide used for the other parts. The tuning element 25 is cylindrical in shape and preferably cup-shaped, and is provided with external threads 26 of a size and pitch to fit the threads 13 in the posts 11 a 11 b, 11 c, 11 d. The tuning element 25 may also be provided with a slot or other opening 27, so that it can be rotated with a tool. We prefer that the tuning element 26 be cup-shaped to permit it to be moved over the coil form 16, and thus provide a greater range of capacity.

A conductive element or can 30 is positioned around the posts 11 a, 11 b, 11 c, 11 dto protect the coil construction, and also to provide a voltage reference point sothat the coil can be tuned. The can 30 is preferably a square structure, made of suitable material such as copper, having four sides and a bottom as shown in FIG. 1. The can 30 may also be provided with a plurality of tabs 31 for holding the can 30 on the base 10. The he can 30 may also be provided with a coupling hole or opening or window 32 (indicated in dashed lines in H0. 1) to permit the coil on the coil form 16 to be coupled to an electrical circuit. However, other coupling elements may be provided if desired.

When a coil is constructed in accordance with our invention, the coil is wound on the coil form 16. The coil form 16 and wound coil is then inserted in the hole 14 in the base, as shown in F IG. 2. The tuning element 25 is then threaded into the receptacle formed by the threads 13, and the conductive element or can 30 is then placed over or around the posts 11 a, 11 b, 11 c, 11 d, and its tabs 31 bent down against the outer surface of the base 10 to hold the can 30 in position. The lower end 22 a of the wire 22 is then soldered or fastened to one of the tabs 31 of the can 30. The top of the can 30 may be provided with a suitable hole or opening 33 to permit a tool to be inserted inside the can 30 and into the slot 27 in the tuning element 25.

the turns of the coil and the conductive element or can 30.

This change in the amount of dielectric material serves to change the capacity between the coil turns 22 and the can 30, so that a tunable coil or resonator is provided. FIG. 3 shows an equivalent electrical circuit of such a tunable coil or resonator. ln H6. 3, the coil is illustrated by an inductive symbol, and is shown connected to the can 30 by the tab 31. The variable capacitive element is diagrammatically illustrated as being connected between the can 30 and the upper end 22 b of the coil, although it is to be understood that this capacitive element actually exists between all of the coil turns and the can 30. However, we have shown the capacitive element connected to the end 22 b, since the greatest capacity change takes place at this end 22 b because of the shape or configuration of the tuning element 25.

We have built a number of embodiments of our coil construction, and have found that it operates satisfactorily in various applications. In one embodiment, the coil construction was intended to be used as a frequency of 450 megacycles. The can 30 had a square cross section measuring 0.375 by 0.375 inches, and was 0.66 inch high. The coil form 16 had a length of 0.31 inch, and a diameter of 0.25 inch. The coil form 16 was wound with 7 %turns which provided a coil having an unloaded Q of 425 at a frequency of 470 megacycles. The coil could be tuned between 420 and 470 megacycles, with a 0.1 inch travel of the tuning element. Thus, our construction is small, and easily built. In addition, it provides a fairly wide range of tuning, and is rugged in its construction.

While we have shown only one embodiment of the invention, persons skilled in the art will appreciate that modifications may be made. For example, the coil form 16 may have various types of slots or notches to receive and hold the ends of the wire forming its coil. The tuning element 25 may have other shapes, although we prefer a cup-shaped element. And, various types of openings or holes may be used for receiving a tool to adjust the tuning element. Therefore, while the invcntion has been described with reference to a particular embodiment, it isto be understood that modifications may be made without departing from the spirit of the invention or from the scope of the claims.

What We claim as new and desire to secure by Letters Patent of the United States is: i

1. An improved coil construction for radio frequency apparatus comprising:

a. a base of dielectric material;

b. a coil wound about a longitudinal axis and positioned on said base with said longitudinal axis extending upwardly from said base;

. at least three posts of dielectric material positioned on said base around said coil, saidposts extending upwardly from said base in a direction generally parallel to said longitudinal axis, and said posts being threaded on an inner face thereof to provide a threaded receptacle around said longitudinal axis;

. a conductive can positioned around said posts; and

. a tuning element of dielectric material having external threads arranged to fit said threaded receptacle provided by said posts, said tuning element being rotatable in said threaded receptacle to move along said longitudinal axis to vary the amount of dielectric material between said coil and said conductive can.

2. The improved coil construction of claim 1, and comprising four substantially similar dielectric posts respectively positioned at the four corners of a square on said base, said posts extending upwardly from said base in a direction generally parallel to said longitudinal axis and being threaded on an inner face to provide a threaded receptacle around said longitudinal axis.

3. The improved coil construction of claim 2, wherein said coil is helically wound on a form of dielectric material mounted on said base.

4. The improved coil construction of claim 3, wherein said tuning element is cup-shaped for fitting partially around said coil form.

5. The improved coil construction of claim 1, wherein said posts are symmetrically positioned around said longitudinal axis.

6. The improved coil construction of claim 1, and comprising four substantially similar dielectric posts respectively positioned at the four corners of a square on said base, said posts extending upwardly from said base in a direction generally parallel to said longitudinal axis, and said posts being threaded on an inner face to provide a circular threaded receptacle concentrically positioned around said longitudinal axis.

7. The improved coil construction of claim 6, wherein said tuning element is cup-shaped for fitting partially around said coil form. 

1. An improved coil construction for radio frequency apparatus comprising: a. a base of dielectric material; b. a coil wound about a longitudinal axis and positioned on said base with said longitudinal axis extending upwardly from said base; c. at least three posts of dielectric material positioned on said base around said coil, said posts extending upwardly from said base in a direction generally parallel to said longitudinal axis, and said posts being threaded on an inner face thereof to provide a threaded receptacle around said longitudinal axis; d. a conductive can positioned around said posts; and e. a tuning element of dielectric material having external threads arranged to fit said threaded receptacle provided by said posts, said tuning element being rotatable in said threaded receptacle to move along said longitudinal axis to vary the amount of dielectric material between said coil and said conductive can.
 2. The improved coil construction of claim 1, and comprising four substantially similar dielectric posts respectively positioned at the four corners of a square on said base, said posts extending upwardly from said base in a direction generally parallel to said longitudinal axis and being threaded on an inner face to provide a threaded receptacle around said longitudinal axis.
 3. The improved coil construction of claim 2, wherein said coil is helically wound on a form of dielectric material mounted on said base.
 4. The improved coil construction of claim 3, wherein said tuning element is cup-shaped for fitting partially around said coil form.
 5. The improved coil construction of claim 1, wherein said posts are symmetrically positioned around said longitudinal axis.
 6. The improved coil construction of claim 1, and comprising four substantially similar dielectric posts respectively positioned at the four corners of a square on said base, said posts extending upwardly from said base in a direction generally parallel to said longitudinal axis, and said posts being threaded on an inner face to provide a circular threaded receptacle concentrically positioned around said longitudinal axis.
 7. The improved coil construction of claim 6, wherein said tuning element is cup-shaped for fitting partially around said coil form. 